Question 1

Which virus causes AIDS (Acquired Immune Deficiency Syndrome)?

Accepted Answer

Answer reason: This mechanism explains the hallmark susceptibility to opportunistic infections and certain malignancies. HPV is primarily associated with anogenital warts and cervical and other cancers, not systemic CD4 depletion. Hepatitis B primarily causes liver disease, and influenza causes acute respiratory infection; neither produces the progressive acquired immunodeficiency that defines AIDS.

Question 2

Which disease is caused by the bacterium Vibrio cholerae?

Accepted Answer

Answer reason: Vibrio cholerae colonizes the small intestine and produces cholera toxin, which drives massive chloride and water secretion, leading to profuse watery diarrhea and dehydration. This clinical syndrome is the disease cholera. Typhoid is caused by Salmonella Typhi, dysentery is classically due to Shigella or Entamoeba histolytica, and malaria is due to Plasmodium protozoa transmitted by Anopheles mosquitoes.

Question 3

Which disease is caused by the Plasmodium parasite?

Accepted Answer

Answer reason: This life cycle produces the characteristic febrile paroxysms and can cause anemia, jaundice, and severe complications such as cerebral involvement with certain species. Dengue is caused by a flavivirus, typhoid by Salmonella Typhi, and tuberculosis by Mycobacterium tuberculosis, so they do not match a Plasmodium etiology. Therefore the only option directly caused by Plasmodium is the one selected.

Question 4

A sexually transmitted disease caused by bacteria is ...?

Accepted Answer

Answer reason: Syphilis is caused by the spirochete Treponema pallidum, making it a classic bacterial STD. AIDS is caused by HIV (a virus), so it is not bacterial. Leprosy (Mycobacterium leprae) and pertussis (Bordetella pertussis) are bacterial diseases but are not primarily sexually transmitted.

Question 5

Acid-fast staining is used for identification of which bacteria?

Accepted Answer

Answer reason: Mycobacteria have high mycolic acid content, making them classically acid-fast and identifiable with Ziehl-Neelsen or Kinyoun stains. In contrast, Staphylococcus and Streptococcus are identified primarily by Gram stain and related biochemical tests because they do not have mycolic-acid–rich walls. Salmonella is a Gram-negative bacillus and is not acid-fast, so it would not be targeted by this staining method.

Question 6

The most common mode of transmission of TB is?

Accepted Answer

Answer reason: These particles can remain suspended and be inhaled by others, making respiratory spread the dominant route. Fecal–oral transmission is typical of enteric pathogens, not Mycobacterium tuberculosis. Direct skin contact and sexual contact are not common mechanisms for TB spread in routine community transmission.

Question 7

Which bacterium causes whooping cough?

Accepted Answer

Answer reason: The organism responsible is a small gram-negative coccobacillus that adheres to ciliated respiratory epithelium and disrupts mucociliary clearance. The other options are associated with different syndromes: Haemophilus influenzae with otitis media/epiglottitis (type b historically), Neisseria meningitidis with meningitis/septicemia, and Corynebacterium diphtheriae with pseudomembranous pharyngitis and systemic toxin effects. Therefore the best match for the etiology of pertussis is the first option.

Question 8

Which fungus is associated with tinea versicolor?

Accepted Answer

Answer reason: This organism’s yeast form on KOH classically shows “spaghetti and meatballs” (hyphae with spores), supporting its role in this condition. Dermatophytes such as Trichophyton rubrum and Epidermophyton floccosum primarily cause tinea corporis/pedis/cruris by invading keratinized tissues, not tinea versicolor. Candida albicans more commonly causes mucocutaneous candidiasis (thrush, intertrigo) rather than the pigmentary changes typical of tinea versicolor.

Question 9

Which fungus is associated with candidiasis?

Accepted Answer

Answer reason: The organism most classically responsible for thrush, vulvovaginal candidiasis, and cutaneous/intertriginous yeast infections is this commensal yeast, especially with antibiotic use, diabetes, or immunosuppression. In contrast, Sporothrix schenckii causes lymphocutaneous sporotrichosis after traumatic inoculation from plants/soil, not candidiasis. Aspergillus fumigatus is associated with invasive aspergillosis or allergic bronchopulmonary disease rather than mucocutaneous yeast infections.

Question 10

Which organism is most commonly associated with peptic ulcer disease?

Accepted Answer

Answer reason: This organism colonizes the stomach lining (via urease activity and motility), causing inflammation and predisposing to duodenal and gastric ulcers. The other listed bacteria are classically associated with different syndromes (e.g., watery diarrhea with cholera, skin/soft tissue and toxin-mediated disease with staphylococci), not ulcer formation. Identifying the correct pathogen matters clinically because eradication therapy significantly reduces ulcer recurrence and complications like bleeding.

Question 11

Patient has been diagnosed with a urinary tract infection. What is the most likely cause of this infection?

Accepted Answer

Answer reason: E. coli is the predominant uropathogen because its adhesins (e.g., P fimbriae) promote attachment to uroepithelium and persistence despite urine flow. Enterococci are also recognized causes of UTIs, particularly in healthcare-associated settings, making this combined option the best match among the choices. Neisseria gonorrhoeae primarily causes urethritis/cervicitis rather than typical cystitis, and beta-hemolytic streptococci and Staphylococcus aureus are less common primary causes of uncomplicated UTIs.

Question 12

Fever, whooping cough, bod, ache are the clinical features of-?

Accepted Answer

Answer reason: The distinctive whoop is the key discriminator among the listed vaccine-preventable diseases. Diphtheria more typically presents with sore throat and a gray pseudomembrane, not a classic whoop. Measles and mumps have hallmark features such as rash/Koplik spots or parotitis, respectively, rather than whooping paroxysms.

Question 13

Which of the following spreads through contaminated food or water?

Accepted Answer

Answer reason: Vibrio cholerae is acquired through ingestion of contaminated water/food and can rapidly cause severe dehydration due to toxin-mediated fluid loss. In contrast, tetanus results from wound contamination with spores, rabies is transmitted via animal bites/saliva, and tuberculosis spreads primarily through airborne droplet nuclei. Therefore the only option matching food/water transmission is the correct one.

Question 14

A 40-year-old man with AIDS and a CD4 count of 80/mm3 has a fever and a right lower lobe infiltrate. Which of the following organisms would be considered to be the most likely cause of his pneumonia if recovered from BAL fluid (bronchoalveolar lavage)?

Accepted Answer

Answer reason: Legionella is a recognized cause of severe pneumonia in immunocompromised patients and is classically diagnosed from lower respiratory specimens (including BAL) using culture on specialized media or antigen/PCR. Cytomegalovirus can be detected in BAL but often represents colonization/reactivation rather than the primary cause of a focal lobar pneumonia; true CMV pneumonitis is typically diffuse/interstitial with hypoxemia. Candida in respiratory samples is usually colonization, and HSV pneumonia is uncommon and usually in critically ill/intubated patients, making them less likely primary causes here.

Question 15

What is the most common cause of bacterial vaginosis?

Accepted Answer

Answer reason: The organism most commonly associated with this dysbiosis in exam questions is Gardnerella vaginalis, which correlates with clue cells and a fishy (amine) odor. Escherichia coli is a common uropathogen and can cause some genital infections but is not the typical cause of BV. Staphylococcus aureus and Streptococcus pneumoniae are not characteristic vaginal pathogens for BV and are more associated with skin/soft tissue and respiratory infections, respectively.

Question 16

What is the most common cause of meningitis in adults?

Accepted Answer

Answer reason: pneumoniae due to its frequent nasopharyngeal colonization and invasive potential, especially in older adults and those with comorbidities or asplenia. This organism commonly causes otitis media/sinusitis and pneumonia that can seed the meninges hematogenously. N. meningitidis is also important in adolescents/young adults and outbreak settings, but overall it is typically less common than pneumococcus in adults. E. coli is more characteristic of neonatal meningitis, and H. influenzae has markedly decreased in vaccinated populations and is more associated with pediatric disease.

Question 17

Influenza disease is caused by which of the following?

Accepted Answer

Answer reason: The causative agent is identified by the disease’s transmission pattern (droplet/airborne-range exposure) and typical viral syndrome features such as abrupt fever, myalgias, and cough. Bacteria are more associated with secondary complications (e.g., bacterial pneumonia) rather than the primary cause of influenza. Fungi and protozoa do not cause the classic seasonal influenza illness.

Question 18

Which bacterium is the most common cause of traveler’s diarrhea?

Accepted Answer

Answer reason: This mechanism leads to acute, noninflammatory diarrhea without prominent fever or blood, matching the classic presentation in travelers. By contrast, Salmonella typhi is associated with systemic enteric fever, Shigella more often causes inflammatory dysentery with blood/tenesmus, and Vibrio cholerae classically causes profuse “rice-water” stools but is not the most common overall cause of traveler’s diarrhea. Therefore, the organism most frequently implicated is the enterotoxigenic strain of E. coli.

Question 19

Which of the following is a fungal disease?

Accepted Answer

Answer reason: This condition is commonly termed tinea and is transmitted by direct contact with infected people, animals, or fomites. By contrast, cholera and typhoid are bacterial enteric infections, and tuberculosis is a bacterial infection caused by Mycobacterium tuberculosis. Therefore, the only fungal disease listed is the dermatophyte infection.

Question 20

Which disease is caused by the bacterium Mycobacterium tuberculosis?

Accepted Answer

Answer reason: Mycobacterium tuberculosis is an acid-fast bacillus that causes a chronic granulomatous infection most commonly involving the lungs, with potential for extrapulmonary spread. Malaria is caused by Plasmodium species (a protozoan), while AIDS is caused by HIV (a virus), so those do not match the bacterial organism given. Cancer is not caused by this bacterium, though chronic infections can be associated with malignancy risk in other contexts.

Train with a large NCLEX question bank and jump into a full exam-style simulator

Microbiology Practice Test 41

Microbiology NCLEX Practice Test

Continue Learning